1. Field of the Invention
The present invention relates to a motor drive device that is implemented in a control panel, such, for example, as a heavy electrical control panel of an NC machine tool. In particular, the present invention relates to a motor drive device including a motor control unit, a heat sink attached to the motor control unit, and a fan motor for cooling the heat sink, wherein the fan motor is removably mounted, and a control panel including such a device.
2. Description of the Related Art
In a motor control unit of the motor drive device that is implemented in the control panel, there is mounted a heat sink for heat dissipation. The cooling effect of the heat sink is enhanced by disposing the fan motor adjacent to the heat sink.
Further, in order to prevent hot air from being filled in the control panel, sometimes a hole or notch is formed in a rear wall portion of the control panel, dispose the motor control unit of the motor drive device in the control panel, and let only the heat sink attached to the motor control unit via an attaching unit come out of the control panel through a hole or notch of the rear wall portion of the control panel. In such a case, generally, the fan motor for cooling the heat sink is also disposed outside the control panel. The hole or notch of the rear wall portion is closed by the attaching unit of the motor drive device.
In most cases, since the control panel is provided adjacent to a wall of a building other machinery or the like, there is almost no space through which a person can pass at the rear side of the control panel. Therefore, it is difficult to get access to the fan motor from the rear side of the control panel to exchange and inspect the fan motor.
Thus, it has been proposed to form a second hole through which the fan motor can be passed in the rear wall portion of the control panel, together with the first hole that permits passage of the heat sink (for example, refer to Japanese Laid-open Patent Publication No. 2009-27776). According to this proposal, it is possible move the fan motor existing at the rear side of the control panel to the front side (front face) of the control panel through the second hole, thereby inspecting and exchanging the fan motor. Alternatively, it is sometimes the case that a hole through which the heat sink and the air blower can be passed together is formed in the rear wall portion of the control panel and an additional hole through which the air blower can be passed is formed in the attaching unit of the motor drive device.
Furthermore, in Japanese Patent No. 5312012 and Japanese Patent No. 3404907, a structure has been proposed in which for the purpose of maintenance of the device, a duct provided between an air blowing fan and a heat generating component is made attachable and removable.
However, the above-described conventional technique has problems as follows. The problems of the conventional technique will now be described based on FIG. 6. FIG. 6 is a top view schematically illustrating a main portion of a conventional motor drive device which is implemented in a control panel.
According to FIG. 6, a motor control unit 102 of a motor drive device which is implemented in a control panel 101 is attached to a front face 103a of a rear wall portion 103 of the control panel 101. A hole or notch 103b is formed in the rear wall portion 103 of the control panel 101. A heat sink 104 attached to the motor control unit 102 is disposed outside the control panel 101 (particularly, at the rear side of the control panel 101) through the hole or notch 103b. A fan motor 105 is disposed on the upper end of the heat sink 104 disposed at the rear side of the control panel 101. With such a structure, in order to attach or remove the fan motor 105 from the front side (front face) of the control panel 101, it is required that the fan motor 105 be passed through the hole or notch 103b in the rear wall portion 103 of the control panel 101. Therefore, it is necessary to select, as the fan motor 105, a fan motor which is smaller than the notch 103b in the rear wall portion 103 of the control panel 101. In other words, as illustrated in FIG. 6, the size A of the fan motor 105 cannot be made larger than the size B of the notch 103b, so that usable fan motors are limited.